This application was filed under 35 U.S.C. 371 from PCT/US93/11968 filed Dec. 9, 1993.
The present invention relates to permalloy films and more particularly to an amorphous permalloy film which can be used in magnetic recording systems.
A recent trend in magnetic storage system design is the use of magneto-resistive (MR) heads to read data from a magnetic storage medium in a magnetic storage device. Use of MR heads, instead of inductive sensor heads, has enabled manufacturers to increase recording densities in magnetic storage systems. Various materials and methods of fabricating thin films from these materials are being used to produce MR heads which can be used to meet the higher recording density requirements which will be needed in future magnetic storage systems.
Permalloy is a name for any of a large number of highly magnetically permeable alloys containing a combination of nickel and iron. Permalloy is frequently used as magnetic circuit material for applications such as thin film MR heads because of its high magnetic permeability and its superior frequency characteristics. Specifically, permalloy has been used as a thin film magneto-resistive element (MRE) in MR heads. The MRE of a thin film MR head is the portion which exhibits a change in resistance as it passes through magnetic fields emanating from the magnetic storage media and other favorable magnetic and electrical properties.
Although many magnetic films are currently made from permalloy, other types of materials are also frequently used. For example, amorphous materials have been used to make magnetic thin films because of their advantageous properties, particularly with regard to magnetic properties. These amorphous materials usually have naturally occurring amorphous or nearly amorphous crystalline structures. Examples of naturally occurring amorphous materials used in thin film magnetic heads includes CoZr, CoZrRh, and CoZrNb. These essentially amorphous materials are frequently used in thin film magnetic heads because of their high magnetic permeability and other favorable magnetic and electrical properties.
Ion-beam sputtering is a technology which is being increasingly used in the deposition of thin films, and particularly in the deposition of MREs for MR head magnetic storage devices. Ion-beam sputtering deposition techniques employ collimated beams of nearly monoenergetic ions which are directed and focused onto a target up to 60 cm (24 inches) away from the source of ion generation. The large separation distance between the target and the ion or plasma generation region allows ion-beam sputtering to be conducted at significantly lower pressures than other standard sputtering techniques such as rf-diode sputtering techniques. The lower pressures translate to fewer collisions between ions in the ion-beam and gas molecules before the ions collide with the target. This results in higher energy films. The reflection of ions and neutrals from the target also helps increase energy levels of the thin films fabricated using ion-beam sputtering techniques. Consequently, ion-beam sputtered thin films exhibit higher densities, improved corrosion resistance, reduced impurity levels and altered stresses in comparison to films sputtered under standard techniques such as rf-diode sputtering.
Ion-beam sputtering has been used in various thin film applications such as optical coatings, fabrication of magneto-optic media and fabrication of MR heads. Ion-beam sputtered MREs have shown higher outputs and greater corrosion resistance than rf-diode sputtered MREs.
Ion-beam techniques have been used to deposit a number of different thin film materials. For example, high permeability amorphous materials such as CoZr, CoZrRh and CoZrNb have been successfully deposited by ion-beam sputtering techniques. Additionally, ion-beam sputtering of permalloy, or NixFe1xe2x88x92x, has been used to obtain permalloy films with improved characteristics. Several articles have been written on the properties of ion-beam sputtered permalloy films.
A first article, by Jerry Lo et al., is entitled xe2x80x9cMagnetic and Structural Properties of High Rate Dual Ion-Beam Sputtered NiFe Filmsxe2x80x9d, Journal of Applied Physics, Vol. 61, No. 8, Apr. 15, 1987. In this article, the authors noted that by varying the target angle relative to the substrate surface, the magnetic properties of the Nixe2x80x94Fe films can be altered. The authors also found that no significant changes in magnetic and electrical properties were observed in films deposited with beam voltages between 200 and 2,000 V (beam energies between 200 and 2,000 electron-volts). This article also discussed the results of adding nitrogen to the sputtering process to reduce the x-ray diffraction  less than 111 greater than  peak. Ultimately, the authors concluded that, in the case of sputtering without the addition of nitrogen, the x-ray diffraction  less than 111 greater than  peak intensity remained relatively constant for diffraction angles of less than 45xc2x0, and that this implies that the Nixe2x80x94Fe films with diffraction angles of less than 45xc2x0 have similar  less than 111 greater than  textures.
A second article, by Christopher V. Jahnes et al., is entitled xe2x80x9cIon Beam Sputter Deposited Permalloy Thin Filmsxe2x80x9d, IEEE Transactions on Magnetics, Vol. 28, No. 4, July 1992. In this article, the authors describe the ion-beam sputtering procedures used in their research and discuss the properties of the resulting ion-beam sputter deposited permalloy films. The authors of that paper noted that, under certain conditions, ion-beam sputtering could be used to deposit permalloy films with characteristics suitable for use in thin film heads. In this article, the authors made a number of observations concerning ion-beam sputtered permalloy films. One important observation was that there is little change in the magnetic properties of ion-beam deposited films as a function of the film deposition rate which is dependent upon the energy level of the ion beam.
A third article, by G. C. Chi et al. is entitled xe2x80x9cThe magnetoresistivity, structure, and magnetic anisotropy of RF sputtered and E-beam evaporated NiFe filmsxe2x80x9d, Journal of Applied Physics, Vol. 52, No. 3, March 1981. In this article, the authors describe the differing structural and magnetic properties of NiFe films formed by RF sputtering and E-beam evaporation. The use of permalloy thin films as bubble detectors is mentioned.
A fourth article, by M. Takahashi et al. is entitled xe2x80x9cFabrication and Magnetic Properties of Thin Films Sputtered on the Substrate Excited by SAWxe2x80x9d, IEEE Translation Journal on Magnetics in Japan, Vol. 6, No. 2, February 1991. In this article, the authors describe the deposition of NiFe films by d.c. magnetron sputtering onto substrates excited by surface acoustic waves. The author found that the physical structure of the film could be made to change dramatically as a function of the excitation amplitude of the surface acoustic waves and that these structural changes altered the magnetic properties of the film.
As recording density requirements continue to increase, magnetic thin films with improved magnetic and electrical properties must be found in order to manufacture MR heads capable of meeting these increasing density requirements. Use of materials such as permalloy films and/or naturally occurring amorphous films must be further developed to achieve higher recording capabilities.
The present invention is based upon the recognition that a thin magnetic film with the desirable magnetic and electrical properties of permalloy films and with increased digital and analog output amplitudes provides an important tool in the design of magnetic storage and recording systems capable of meeting the high density requirements needed for the future. An amorphous or substantially amorphous permalloy film with magnetic and electrical properties similar to magnetic and electrical properties of nonamorphous permalloy films, but with improved output amplitude and noise characteristics, provides a magnetic material which can be used to achieve the desired increased recording densities.
The present invention is a permalloy film with an amorphous or substantially amorphous crystalline film structure. The permalloy film, which has an atomic composition comprising a combination of nickel and iron, is substantially amorphous in the face centered cubic  less than 111 greater than  plane, with the face centered cubic  less than 111 greater than  plane lying substantially parallel to the surface of a substrate. In preferred embodiments of the present invention. the substantially amorphous permalloy film has a composition which includes between 30 and 86 percent nickel.
In some preferred embodiments of the present invention, the substantially amorphous permalloy film is formed by ion-beam sputtering. The ion-beam sputtering is, in preferred embodiments, conducted with ion-beam energies below 500 electron-volts. In at least one preferred embodiment, the substantially amorphous permalloy film is formed by ion-beam sputtering with ion-beam energies of approximately 300 electron-volts. In another preferred embodiment, the substantially amorphous permalloy film is formed by ion-beam sputtering with an angle of incidence between the ion-beam and a permalloy target of approximately 30xc2x0.
In some preferred embodiments, the substantially amorphous permalloy film of the present invention is used as a magneto-resistive element in a magneto-resistive head. In these preferred embodiments, magneto-resistive elements comprised of the amorphous permalloy films exhibit improved output amplitude and noise characteristics.